Understanding Energy: Forms, Conservation, and Sources

We frequently use the word energy. In the late nineteenth century, science endorsed this concept and gave it a more precise meaning. Many properties of matter can be used to define different kinds of energy that can transform into each other and transfer from some bodies to others.

Kinetic and Potential Energy

An object in motion can collide with another and produce changes. This is known as kinetic energy and can be expressed mathematically as: E_c = 1/2mv². An object located at a certain height may fall, start moving, and push another. This is gravitational potential energy, and we can write it as: E_p = mgh.

Energy Conservation

Energy is conserved in any transformation. If an object falls from a height, it loses potential energy, but that energy does not disappear; it transfers into the soil. Some forms of energy are more useful than others. Seawater contains an enormous amount of thermal energy, but we cannot use it because it is so widely distributed.

Mechanical Work and Energy

If we let ourselves fall, Earth's kinetic energy draws us with our weight. To measure the changes of energy, we use the concept of mechanical work. Mechanical work is calculated by multiplying the force by the distance traveled by the body in the direction of the force: W = Fd. Its unit in the International System is the joule. Mechanical energy is the sum of the kinetic and potential energy possessed by a body: E_m = E_c + E_p. Mechanical energy remains constant when the transformation operates only on weight. The conservation of mechanical energy allows you to simplify calculations that would otherwise be difficult.

Thermal Energy and Heat

The atoms and molecules that make up matter are in continuous motion, a phenomenon known as thermal agitation, and we perceive it as temperature. When two bodies with different temperatures come together, an energy exchange occurs, which only stops when they reach thermal equilibrium and have the same temperature. Heat is a process of transferring thermal energy between bodies in contact. The amount of energy transferred used to be called "heat energy".

Joule's Experiment and Energy Equivalence

Benjamin Thompson investigated heat treatment with a very precise balance. Prescott James Joule devised an experiment to confirm this idea and estimate the amount of heat that could be extracted from mechanical work. Heat and work are two equivalent processes. In his honor, the International System unit of energy is called the joule.

Renewable and Non-Renewable Energy Sources

Both coal and oil have accumulated over millions of years on Earth. They cannot be renewed, and reserves are limited. These are called non-renewable energy sources. Others, like sunlight or wind, will always be available and are called renewable energy sources. The energy contained in energy sources before transformation and distribution is called primary energy. Once transformed, the new form is called an energy carrier. Non-renewable energy sources include fossil fuels, which constitute three-quarters of the primary energy used worldwide, and nuclear energy. Some substances may undergo a process called nuclear fission, in which their atoms disintegrate into lighter atoms. Renewable energy sources include hydro, wind, solar photovoltaic, and solar thermal.

Environmental Impact of Energy Use

The massive use of different energy sources changes our physical environment and produces changes on the planet. Currently, burning fossil fuels pollutes cities and releases gases into the atmosphere that alter the Earth's climate.